Pump-and-nozzle assembly for injecting fuel in internal combustion engines

ABSTRACT

There is described a pump-and-nozzle assembly which forms part of a fuel injection apparatus serving an internal combustion engine and which includes a reciprocating pump piston, the angular position of which determines the injected fuel quantities during the delivery strokes. The pump piston is driven by a servo piston which is intermittently exposed to pressurized fuel delivered by a pressure source. The intermittent admission of pressurized fuel to the servo piston is controlled by a valve plunger which is exposed to pressurized fuel for periods controlled by a solenoid valve.

[ Mar. 12, 1974 EE AA 22 33 33 22 3,592,177 7/1971 Wehpe...........................

1 PUMP-AND-NOZZLE ASSEMBLY FOR .6 Yb 6n he h TS O9 45 99 ll 22 7 54 0 2 O2 97 22 INJECTING FUEL IN INTERNAL COMBUSTION ENGINES 3,363,574 l/1968 Aldinger.....................:.t. 123/32 AE FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Heinz Links, Stuttgart, Germany Assignee: Robert Bosch GmbH, Stuttgart 1,070,442 1/1955 Gennany..... 123/139 Germany [22] Filed: May 26, 1972 Primary ExaminerLaurence M. Goodridge 1 pp No 257 386 Assistant ExaminerRonald B. Cox

Attorney, Agent, or FirmEdwin E. Greigg Foreign Application Priority Data May 28, 1971 [57] ABSTRACT There is described a pump-and-nozzle assembly which forms part of a fuel injection apparatus serving an in- Germany....................

temal combustion engine and which includes a reciprocating pump piston, the angular position of which determines the injected fuel quantities during the delivery strokes. The pump piston is driven by a servo piston which is intermittently exposed to pressurized [56] References Cited UNITED STATES PATENTS fuel delivered by a pressure sourcerThe intermittent 111.. 123/32 AE 123/32 AE French 2,310,773 Fuscaldo 3,665,907 Laufer.........

3,587,547 Hussey 3,501,099 970 Benson PATENTEWR I 2 1974 3,796, 206

sum 2 or s Pmmmm 12 mm 3.796; 206

MEI a (If 6 PAIENTEU MAR 12 1974 SHEH 0F 6 PUMP-AND-NOZZLE ASSEMBLY FOR INJECTING FUEL IN INTERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION This invention relates to a pump-and-nozzle assembly for injecting fuel in internal combustion engines, particularly diesel engines. The assembly is of the type that has a pump piston which is driven by a servo piston having a diameter greater than that of the pump piston. The assembly is coupled to a pressure source which supplies fuel to both the pump piston and the servo piston and wherein, in phase with the engine operation, an electromagnetically operated valve plunger directs, in its first position, a fuel flow to the servo piston and, in its second position, a fuel flow from the servo piston into a discharge conduit. Thus, when moved into its first position, the valve plunger triggers the start of fuel injection, while, when moved into its second position, it effects the start of the return stroke. The terminal moment of the injection and the injection quantities are determined by the angular position of an oblique control edge which is provided on the pump piston and which cooperates with a control bore in the pump cylinder.

In a known pump-and-nozzle assembly of the aforenoted type, such as disclosed for example in US. Pat. No. 2,598,528, the valve plunger is mechanically connected with the armature of the electromagnet and is moved thereby into either of its switching positions. This arrangement has the disadvantage that the inertia of the armature and the valve plunger renders a sufficiently rapid and accurate operation difficult or even impossible particularly in case of fast-running diesel engines.

Since the magnet for switching the valve plunger into either switching position has to execute large strokes and because the masses to be moved are of voluminous structure, it is a further disadvantage that this magnet has a relatively long delay of response and a much too long switching period.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention to eliminate the aforedescribed disadvantages and to provide a solenoid valve-controlled pump-and-nozzle assembly which operates sufficiently rapidly and accurately for fastrunning diesel engines.

Briefly stated, according to the invention, the valve plunger is exposed to a branched-off part of pressurized fuel serving as auxiliary control liquid and pressurized by a pressure source. The admission of said pressurized fuel to, and its withdrawal from said valve plunger is regulated by electromagnetically controllable valve means.

The invention will be better understood, as well as further objects and advantages become more apparent, from the ensuing detailed specification of two exemplary embodiments taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal sectional view of the first embodiment of the pump-and-nozzle assembly;

FIG. 2 is a partially sectional view along line IIII of FIG. 1;

FIG. 3 is a longitudinal schematic sectional view of the pump-and-nozzle assembly according to FIGS. 1 and 2 shown with associated components of the entire fuel injection apparatus in the first switching position of the valve plunger at the beginning of the delivery or pressure stroke;

FIG. 4 is a view similar to that of FIG. 3 showing the fuel injection apparatus subsequent to the end of the delivery stroke;

FIG. 5 is a view similar to FIG. 3, of a second embodiment in its position at the beginning of the delivery stroke;

FIG. 6 is a view similar to FIG. 5 showing the fuel injection apparatus in a position it assumes upon completion of the delivery stroke and FIG. 7 is a schematic sectional view of a modified component forming part of the structure illustrated in FIG. 3.

DESCRIPTION OF THE FIRST EMBODIMENT Turning now to FIGS. 1 and 2, there is shown a pump-and-nozzle assembly 9 which, in essence, is formed of two structural groups that constitute a coherent, rigid unit by virtue of an externally threaded clamping sleeve 11 tightened to a housing 10.

The first structural group is formed of a hydraulically driven pump 13 which is controlled by a valve plunger 12. The pump 13 has a servo piston 14, a pump piston 15, a pump cylinder 16 and a pressure valve 17. The

alve plunger 12 is controlled by means of an electromagnetically actuated 3/2-way valve 18 hereinafter referred to as a solenoid valve. The control of the fuel quantities delivered by the pump is effected in a known manner by means of a fuel setting device including a fuel rack 19 and a pinion sleeve 20. By means of the setting device 19, 20 the pump piston 15, having a cylindrical control face 22 bounded by an oblique control edge 21, can be set into different angular positions. In each angular position of the pump piston 15, a different range of the control face 22 cooperates with a control bore 23 in the pump cylinder 16. For purposes of hy draulic force equalization and unobstructed fuel flow, the pump 13 may be provided in a known and nonillustrated manner with two control edges 21, two control faces 22 and two control bores 23. The supply of fuel to the pump work chamber 24 is separate from the return flow of the non-injected fuel and is effected through fuel supply bores 25 which are supplied with fuel by a supply conduit 26. The fuel supply bores 25 merge into an annular channel 27 provided in the wall of the cylinder bore 28 that receives the pump piston 15.

In the upper dead center position of the servo piston 14 and the pump piston 15 shown in FIG. 1, a supply control edge 31 bounding an annular groove 29 of the pump piston 15, opens the annular channel 27 (which serves as a supply channel) only by a narrow throttle gap a so that'the fuel may flow in a throttled manner into the pump work chamber 24 through the annular groove 29 and an axial lateral groove 32 which is prothrough the control bore 23 and a return conduit 33 in a depressurized manner back to a fuel tank until, during the delivery stroke (that is, the downward movement) of the piston 15, the control face 22 closes the control bore 23.

The exposure of the pump work chamber 24 to the rinsing effect of the fuel flow while the pistons 14 and 15 are in their upper dead center position, cools the pump-and-nozzle assembly in an advantageous manner, thus largely preventing the formation of highly undesirable vapor bubbles. Occasionally formed bubbles are, during this rinsing contact, torn away and carried to the fuel tank. The fuel delivered under pressure during the delivery stroke of the pump piston 15 leaves the pump work chamber 24 through the pressure valve 17.

To the pressure valve 17 which is formed of a valve body 36, a movable valve member 37 and a valve spring 38, there is coupled, in an axial direction of the pump-and-nozzle assembly 9 the second structural group constituted by a fuel injection nozzle 41 which includes a spring housing 42 and a nozzle body 43. In the latter there is guided a nozzle needle 44 on which, within a spring chamber 45 of the spring housing 42, there is inserted a spring seat disc 46 that supports one end of a closing spring 47. The closing spring 47 tends to maintain the nozzle needle 44 in its closed position as shown in FIG. 1 and engages with its other end an insert member 48 the dimensions of which determine in a known manner both the spring bias and the needle stroke.

From the pressure valve 17 there extend serially arranged conduit portions 49 and 51 to an annular chamber 52 in which the pressurized fuel affects an annular work face 53 of the nozzle needle 44.

For returning leakage fuel into the fuel tank, the spring chamber 45, an oil leakage groove 54 in the pump cylinder bore 28, a second spring chamber 55 below the servo piston 14 and a third spring chamber 56 below the valve plunger 12 are in communication (not shown in part) with a fuel leakage bore 57 connected to the fuel tank.

The pinion sleeve of the setting device 19, 20 is rotatably supported on a cylindrical extension 58 of the pump cylinder 16 and guides, by means of slots 59, a lug 61 of the pump piston 15. When by virtue ofa longitudinal displacement of the toothed fuel rack 19 the pinion sleeve 20 provided with teeth 62 is rotated, the pump piston 15 executes a rotary motion in the same sense and, as a result, another range of the control face 22 will cooperate during the strokes of the pump piston 15 with the control bore 23. Consequently, a different fuel quantity will be injected.

A foot 63 of the pump piston 15 is held in a retaining plate 64 which is pressed by means of a spring 65 against the base face 66 of the cup-shaped servo piston 14. The spring 65 which tends to maintain the servo piston 14 in its position shown in FIG. ll, engages an internal shoulder of the housing 10 through an annular spring seat disc 68. The latter also prevents an axial displacement of the pinion sleeve 20, while it permits a rotation thereof.

The valve plunger 12 is moved into and maintained in the position shown in FIGS. 1 and 2 by means of a spring 69 when the control pressure chamber 71 above a small control piston 72 is in a depressurized condition. The control piston 72 is guided in a housing insert 73 and has a cross section which is substantially (preferably several times) smaller than that of the valve plunger 12. This feature has the advantage that for moving the valve plunger 12 there is required only a small fuel quantity as control liquid so that the switching periods of the solenoid 18 may be short. A further advantage resides in the fact that the solenoid valve 18 (FIG. 2) may be of small dimensions by virtue of which the switching periods may be additionally shortened.

As shown in FIG. 2, the solenoid valve 18 which is disposed in the upper part of the housing 10 in a stepped mounting bore 74 arranged coaxially with a controlconduit portion 75, is pressure-equalized and actuated by means of an electromagnet 76. The control conduit portion 75 is laterally coupled to an annu lar channel 77a of a servo supply conduit 77 (FIG. 1). The flow of the servo liquid, which in the present case is fuel, through the conduit portion 75 is controlled by the solenoid valve 18. In one of the switching positions, as discussed later in connection with FIG. 4, the solenoid valve 18 directs the servo liquid through a control conduit 78 to the control pressure chamber 71 and in its other switching position (FIGS. 2 and 3) it directs the servo liquid from the control pressure chamber 71 into a return or discharge conduit 79 and simultaneously blocks the flow from the conduit portion 75.

The solenoid valve 18 has a valve housing 80 and includes, as the movable valve member, a sphere 81 which, in its position shown in FIG. 2, engages a valve seat 82 and thus closes a port 83, so that the supply of fuel to the control pressure chamber 71 is blocked. Simultaneously, the control pressure chamber 71 is in communication with a discharge conduit 79 through a second valve seat 82 which is shown in an open position in FIG. 2.

The electromagnet 76 is provided with an armature 85 which is guided in the valve housing in axial alignment with the port 83 and which, under the effect of a spring 87, presses, by means of an integral pin 86, the sphere 81 against the valve seat 82 when the electromagnet 76 is in a de-energized condition. In order to permit the use of the spring 87 of moderate strength at the high servo pressure (for example, p, 50 kg/cm the solenoid valve 18 is pressure-equalized by providing a channel 88 which communicates the pressure prevailing in the control conduit portion 75 to a chamber 89 located behind the armature 85 and accommodating the spring 87. The surface of the sphere 81 and thearmature 85 affected by the fuel are of identical magnitude so that the forces which are derived from the liquid pressure and which urge the sphere 81 in the opening and closing direction are also equal. Therefore, the force of the spring 87 has to be sufficient merely to maintain the sphere 81 in contact with the valve seat 82.

As soon as the solenoid 91 of the electromagnet 76 is energized, for example, by means of an electronic control apparatus described in connection with FIGS. 3-6, the force of the spring 87 is overcome by the electromagnetic forces and the armature 85 is displaced. The fuel now flowing through the first valveseat 82 presses the sphere 81 against the second valve seat 84 and, as a result, the fuel may flow from the control conduit portion 75 through the port 83 and the control conduit 78 into the servo pressure chamber 71. The portions of the valve housing 80 which are under different high pressures are sealed from one another in the stepped mounting bore 74 by means of packing rings 92, 92a and 92b.

The valve plunger 12 is coupled in a forcetransmitting manner to the small control piston 72 only through the spring 69. The valve plunger 12 has an annular groove 93 which permits a fuel flow in the position whown in FIG. 1 (also FIG. 3) from the annular groove 770 through a connecting conduit 94 to a servo pressure chamber 95, or in the other switching position (FIG. 4) permits a fuel flow from the servo pressure chamber 95 through the conduit 94 into an annular chamber 96 (FIG. 1) bounded by the valve plunger 12. To the return conduit 33 there extends from the annular chamber 96 a return bore 98 shown in broken lines in FIG. 2 and closed by a plug 97. The return conduit 33, the supply conduit 26 and the fuel leakage bore 57 end on the outer face of a coupling flange 99. The outwardly extending discharge conduit 79, as shown in FIG. 2, may also extend within the housing to the annular chamber 96 wherefrom the fuel, returning from the control chamber 71, may flow through the return bore 98 to the return conduit 33. The servo pressure chamber 95 is closed by a threaded cap 101 (FIG. 1) which has an abutment screw 102 for determining the upper dead center position of the servo piston 14.

Turning now to FIG. 3, the servo piston 14, the pump piston 15, the valve plunger 12 and the control piston 72 are in their upper position also shown in FIG. 1. The electromagnet 76 is in a de-energized condition and the solenoid valve 18 closes the control conduit portion 75 and depressurizes the control chamber 71 through the control conduit 78 to the return conduit 79. The valve plunger 12 connects the servo supply conduit 77 fed by a pressure source 105, by means of the annular groove 93 with the servo pressure chamber 95 through the connecting conduit 94. The pressure source 105 which may be, for example, a gear pump driven by the internal combustion engine 106, generates a constant pressure p regulated by a pressure regulating valve 107 in a pressure conduit 108, and draws fuel from a fuel tank 111 through a filter 109. The pressure regulating valve 107 has a control location 121 which is controlled in a conventional manner by a movable valve member 112 and through which the excess fuel flows to the return conduit 79 by way of a conduit portion 79a. The servo pressure p 5 may also be controlled in an rpm dependent and/or load dependent manner by designing the pressure control valve 107 accordingly. The load dependency may be achieved, for example, in a known manner by varying the spring bias of the pressure control valve 107 as a function of the position of the accelerator pedal or, as illustrated in a simplified manner in FIG. 7, by means of turning the movable valve member 112' which forms part of the pressure control valve 107 and which is provided with an oblique overflow control edge 122. The rpm dependency is achieved by designing the control location 121 as a throttle regulated by the valve member 112. In this connection reference is had to US. Pat. to Aldinger, No. 3,363,574 issued Jan. 16, 1968. By means of the aforedescribed control of the servo pressure the injection period can be lengthened at small loads or small rpms.

In the position shown in FIG. 3, one part of the fuel, as it has already been described in connection with FIG. 1, flows through the supply conduit 26 into the pump work chamber 24 and therefrom back into the fuel tank 11 1 through the return conduit 33. The return conduit 79 controlled by the solenoid valve 18 directs the fuel quantities flowing out of the control pressure chamber 71 back into the fuel tank 111; in the present embodiment this also occurs through the return conduit 33.

For a better understanding of the description that follows relating to the operation of the pump-and-nozzle assembly 9 according to the invention, there are shown in a schematic manner the essential structural groups of the electric control assembly associated with the solenoid valve 18. The latter is controlled through conductors 114 by an electronic control apparatus 115 which, as a function of the rpm signal Un of an rpm sensor 116 driven by the internal combustion engine 106, the position signal Uw of a position sensor 117, the pressure signal Ud of a pressure sensor 118 and the desired value signal Us of a known regulator 119 determines the switching periods of the solenoid valve 18. The position sensor 117 is connected with the fuel rack 19 and the signal Uw transmitted thereby is dependent upon the position of the fuel rack and thus upon the corresponding angular position of the pump piston 15.

The pressure sensor 118 is connected to the pressure regulating valve 107 and generates the pressure signal 7 Ud, for example, as a function of the position ofv the valve member 112. The regulator 119 may be of known mechanical, hydraulic, electrical or electronic design which moves the fuel rack 19 by means of control or connecting members 120 symbolically illustrated in broken lines. By providing that dependent upon the angular position of the pump piston 15, besides the end of the injection the valve plunger 12 may be switched, it is advantageously achieved that the servo piston executes no idling strokes and that a lesser quantity of fuel serving as servo liquid is required.

FIG. 4 is structurally identical to FIG. 3, but shows the solenoid valve 18 in its other switching position and illustrates the control piston 72, the valve plunger 12, the pistons 14 and 15 in their lower dead center position. The solenoid valve 18, the electromagnet 76 of which is now in an energized condition, connects the control conduit portion with the control pressure chamber 71 through the control conduit 78 and, under th effect of the servo pressure p the control piston 72 moves downwardly and displaces the valve plunger 12 into its shown position.- The valve plunger 12, in turnq closes the supply conduit 77 and its annular groove 93 connects, through the connecting conduit 94, the servo pressure chamber 95 with the return bore 98 and the return conduit 33 which directs the fuel back to the fuel tank 1 11 in a depressurized condition. The annular channel 27 supplied by the supply conduit 26 is closed by the pump piston 15. The pump work chamber 24 communicates with the fuel tank 111 through the control bore 23 and the return conduit 33. Thus, the delivery stroke and also the fuel injection are terminated; the servo piston 14 and the pump piston 15 may, under the effect of the spring 65 execute their return stroke until they again reach the upper dead center position shown in FIGS. 1 and 3.

DESCRIPTION OF THE SECOND EMBODIMENT Turning now to FIGS. 5 and 6, the second embodiment shown in a simplified manner has the same structural groups and components as the first embodiment as illustrated in FIGS. 3 and 4. The pump-and-nozzle assembly 9 including the conduits 94, 26 and 33 is shown in FIGS. and 6 in the same position as the first embodiment in FIGS. 3 and 4, respectively.

In FIG. 5, unlike in FIG. 3, the electromagnet 76 is in an energized condition; the solenoid valve connects the control conduit portion 75 through the control conduit 78 with the control pressure chamber 71 and the control piston 72 and the valveplunger 12 are in their lower position. Since, however, the arrangement of the servo supply conduit 77' and the return conduit 98' is reversed with respect to the arrangement of conduits 77 and 98 in FIG. 3, despite the reversed switching position of the valve plunger 12 the servo pressure chamber 95 is, similarly to FIG. 3, connected with the pressure source 105 through conduits 94, 77' and 108.

In the position shown in FIG. 6 the electromagnet 76 is in its de-energized state and the solenoid valve 18 closes the control conduit portion 75 and connects the control pressure chamber 71 with the return conduit 79 and the fuel tank 111. The control piston 72 and the valve plunger 12 are now in their upper terminal position and the valve plunger 12 closes the servo supply conduit 77 and, asin FIG. 4, connects the servo pressure chamber 95 with the fuel tank 111. This connection, however, is effected through the return bore 98.

In the switching position of the solenoid valve 18, the control piston 72 and the valve plunger 12 according to FIGS. 3 and 5, the delivery stroke is initiated, while in the position according to FIGS. 4 and 6, the return stroke starts. Thus, while in the first embodiment (FIGS. 3 and 4) the electromagnet 76 is in a deenergized condition during the delivery stroke, in the second embodiment (FIGS. 5 and 6) the electromagnet 76 is in an energized state for the delivery stroke.

The second embodiment has the advantage that the duration of the energized condition of the electromagnet 76 is shorter than in the first embodiment and that in case of a power failure in the current supply to the electromagnet 76, the solenoid valve 18 depressurizes the control pressure chamber 71. Consequently, the control piston 72 and the valve plunger 12 are shifted by the spring 69 into their upper position of rest, in which the valve plunger 12 connects the servo pressure chamber 95 with the fuel tank 111, so that also the pump piston and the servo piston 14 are moved by the spring into their upper dead center position and are maintained there. Similarly, in case of a failure of the servo pressure, the control piston 72 and the valve plunger 12 as well as the pump piston 15 and the servo piston 14 return into their initial position.

OPERATION OF THE EMBODIMENTS In the first position of the valve plunger 12 shown in FIG. 3 and FIG. 5, the servo pressure chamber is connected, as already noted earlier, with the pressure source and thus a servo pressure p of, for example, 5O kg/cm exerts a force on the radial sectional face of the servo piston 14 and moves the same, together with the pump piston 15, from the shown position in a downward direction against the force of the spring 65. During this delivery stroke first the fuel supply is interrupted by the closing of the gap a and thereafter the control bore 23 is closed by the control face 22 of the pump poston 15. Upon the latter occurrence the injection stroke begins. In the pump work chamber 24 there is generated an injection pressure p,; of, for example, 300 kg/cm which according to the transformation ratio between the servo piston 14 and the pump piston 15 is greater than the servo pressure p of, for example, 50 kg/cm The pump piston 15 forces the fuel from the pump work chamber 24 through the pressure valve 17 and the conduit portions 49, 51 to the annular chamber 52 in the fuel injection nozzle 41. The closing spring 47 of the fuel injection nozzle 41 is, in the present example, biased to an opening pressure of kg/cm Thus, the fuel which exerts a force on the annular face 53 of the nozzle needle 44 with an injection pressure p,; 300 kg/cm overcomes the force of the spring 47 and lifts the nozzle needle 44 off its seat whereby fuel is injected into the engine cylinder.

As shown in FIGS. 4 and 6, the injection is terminated when the oblique control edge 21 of the control face 22 opens the control bore 23 since, with the opening of the control bore 23 the pump work chamber 24 is, through the axial groove 32 of the pump piston 15 and the return conduit 33 discharged to the fuel tank 111. The injection pressure p drops under the nozzle opening pressure, the nozzle needle 44 returns into its closed position and thus the injection is terminated. The pressure valve 17 ensures in a known manner the desired standing pressure in the conduits 49 and 51 of the fuel injection nozzle 41 as a function of the bias of the valve spring 38 and the design of the valve member 112. At, or very shortly after the terminal moment of the injection, the solenoid valve 18 switches, as commanded by the control signal of the control apparatus 115, into its position shown in FIGS. 4 and 6. By virtue of charging (FIG. 4) the control pressure chamber 71 or discharging the same (FIG. 6), the valve plunger 12 switches into its second switching position shown in FIGS. 4 and 6. At the same time, the servo pressure chamber 95 is connected through the connecting conduit 94, the annular groove 93 of the valve plunger 12, the bore 98, (or 98) and the return conduit 33 with the fuel tank 111. Now the delivery stroke H is terminated and under the effect of the spring 65 the pump piston 15 and the servo piston 14 return into their upper dead center position shown in FIGS. 13 and 5. This upper dead center position is indicated in FIGS. 4 and 6 with broken lines. In this position the pump work chamber 24 is charged and rinsed until, by means of switching of the solenoid valve 18 into its position shown in FIGS. 2, 3 and 5, the next delivery stroke begins.

By means of additional energization of the pressure maintaining valve 121 shown in broken lines in FIG. 3, if desired, the residual pressure in the pump work chamber 24 subsequent to the injection step may be maintained at a desired value. i

What is claimed is:

1. A fuel injection pump-and-nozzle assembly forming part ofa fuel injection apparatus serving an internal combustion engine, said assembly being of the type that has (a) a pump piston executing alternating delivery strokes and return strokes, (b) a pump work chamber bounded by said pump piston, (c) a servo piston connected to said pump piston to drive the latter, said servo piston having a diameter greater than that of said pump piston, (d) a pressure source externally of said assembly for delivering fuel under pressure to said assembly, (e) first supply conduit means extending from said pressure source to said pump work chamber, (f) a servo pressure chamber bounded by said servo piston,

pressure source to said servo pressure chamber, (h) discharge conduit means extending from said servo pressure chamber, (i) a valve plunger controlling said second supply conduit means and said discharge eonduit means, said valve plunger being adapted to assume a first switching position for admitting pressurized fuel from said pressure source to said servo pressure chamber and a second switching position for establishing communication between said servo pressure chamber and said discharge conduit means, (j) electromagnetic means for causing said valve plunger to move from one of its switching positions to the other, and (k) means for varying the angular position of said pump piston for altering the quantities of fuel injected by said assembly into said engine during the delivery strokes of said pump piston, the improvement comprising,

A. a third supply conduit means extending from said pressure source to said valve plunger through which pressurized fuel is delivered by said pressure source for causing displacement of said valve plun- B. a solenoid valve in said third supply conduit means for controlling the admission of pressurized fuel to said valve plunger, said solenoid valve constituting said electromagnetic means,

C. a control piston connected to said valve plunger,

and being dis posed in said third supply conduit means between said solenoid valve and said valve plunger, and I D. means for intermittently energizing said solenoid valve, said control piston being intermittently exposed to pressurized fuel delivered by the pressure source, and said valve plunger having a maximum cross sectional area several times greater than that of said control piston.

2. An improvement as defined in claim 1 wherein said solenoid valve is a pressure-equalized 3/2-way valve having a sphere as its movable valve member.

3. An improvement as defined in claim 1, including means for moving said valve plunger into said second position as a function of the angular position of said pump piston simultaneously with the termination of the injection during each delivery stroke.

4. An improvement as defined in claim 1, including means for varying the pressure of fuel in said second supply conduit means as a function of at least one engine parameter. p

5. An improvement as defined in claim 5, wherein said engine parameter is the engine rpm.

6. An improvement as defined in claim 5, wherein said engine parameter is the engine load.

7. An improvement as defined in claim 1, including means to establish communication through a narrow throttle gap between said pump work chamber and said pressure source in the position assumed by said pump piston upon termination of its return stroke.

8. A fuel injection pump-and-nozzle assembly forming part of a fuel injection apparatus serving an internal combustion engine, said assembly being of the type that has (a) a pump piston executing alternating delivery strokes and return strokes, (b) a pump work chamber bounded by said pump piston, (c) a servo piston con- 7 neeted to said pump piston to drive the latter, said servo piston having a diameter greater than that of said pump piston, (d) a pressure source externally of said assembly for delivering fuel under pressure to said assembly, (e) first supply conduit means extending from said pressure source to said pump work chamber, (f) a servo pressure chamber bounded by said servo piston, (g) second supply conduit means extending from said pressure source to said servo pressure chamber, (h) discharge conduit means extending from said servo pressure chamber, (i) a valve plunger controlling said second supply conduit means and said discharge conduit means, said valve plunger being adapted to assume a first switching position for admitting pressurized fuel from said pressure source to said servo pressure chamber and a second switching position for establishing communication between said servo pressure chamber and said discharge conduit means, (j) electromagnetic means for causing said valve plunger to move from one of its switching positions to the other, and (k) means for varying the angular position of said pump piston for altering the quantities of fuel injected by said assembly into said engine during the delivery strokes of said pump piston, the improvement comprising;

A. a third supply conduit means extending from said pressure source to said valve plunger through which pressurized fuel is delivered by said pressure source for causing displacement of said valve plunger,

B. a solenoid valve in said third supply conduit means for controlling the admission of pressurized fuel to said valve plunger, said solenoid valve constituting said electromagnetic means,

C. means for intermittently energizing said solenoid valve, and

a D. means to establish communication through a narraw throttle ap sawei aia ama w'ar'kziiaasa and said pressure source in the position assumed by said pump piston upon termination of its return stroke. 

1. A fuel injection pump-and-nozzle assembly forming part of a fuel injection apparatus serving an internal combustion engine, said assembly being of the type that has (a) a pump piston executing alternating delivery strokes and return strokes, (b) a pump work chamber bounded by said pump piston, (c) a servo piston connected to said pump piston to drive the latter, said servo piston having a diameter greater than that of said pump piston, (d) a pressure source externally of said assembly for delivering fuel under pressure to said assembly, (e) first supply conduit means extending from said pressure source to said pump work chamber, (f) a servo pressure chamber bounded by said servo piston, (g) second supply conduit means extending from said pressure source to said servo pressure chamber, (h) discharge conduit means extending from said servo pressure chamber, (i) a valve plunger controlling said second supply conduit means and said discharge conduit means, said valve plunger being adapted to assume a first switching position for admitting pressurized fuel from said pressure source to said servo pressure chamber and a second switching position for establishing communication between said servo pressure chamber and said discharge conduit means, (j) electromagnetic means for causing said valve plunger to move from one of its switching positions to the other, and (k) means for varying the angular position of said pump piston for altering the quantities of fuel injected by said assembly into said engine during the delivery strokes of said pump piston, the improvement comprising, A. a third supply conduit means extending from said pressure source to said valve plunger through which pressurized fuel is delivered by said pressure source for causing displacement of said valve plunger, B. a solenoid valve in said third supply conduit means for controlling the admission of pressurized fuel to said valve plunger, said solenoid valve constituting said electromagnetic means, C a control piston connected to said valve plunger, and being disposed in said third supply conduit means between said solenoid valve and said valve plunger, and D means for intermittently energizing said solenoid valve, said control piston being intermittently exposed to pressurized fuel delivered by the pressure source, and said valve plunger having a maximum cross sectional area several times greater than that of said control piston.
 2. An improvement as defined in claim 1 wherein said solenoid valve is a pressure-equalized 3/2-way valve having a sphere as its movable valve member.
 3. An improvement as defined in claim 1, including means for moving said valve plunger into said second position as a function of the angular position of said pump piston simultaneously with the termination of the injection during each delivery stroke.
 4. An improvement as defined in claim 1, including means for varying the pressure of fuel in said second supply conduit means as a function of at least one engine parameter.
 5. An improvement as defined in claim 5, wherein said engine parameter is the engine rpm.
 6. An improvement as defined in claim 5, wherein said engine parameter is the engine load.
 7. An improvement as defined in claim 1, including means to establish communication through a narrow throttle gap between said pump work chamber and said pressure source in the position assumed by said pump piston upon termination of its return stroke.
 8. A fuel injection pump-and-nozzle assembly forming part of a fuel injection apparatus serving an internal combustion engine, said assembly being of the type that has (a) a pump piston executing alternating delivery strokes and return strokes, (b) a pump work chamber bounded by said pump piston, (c) a servo piston connected to said pump piston to drive the latter, said servo piston having a diameter greater than that of said pump piston, (d) a pressure source externally of said assembly for delivering fuel under pressure to said assembly, (e) first supply conduit means extending from said pressure source to said pump work chamber, (f) a servo pressure chamber bounded by said servo piston, (g) second supply conduit means extending from said pressure source to said servo pressure chamber, (h) discharge conduit means extending from said servo pressure chamber, (i) a valve plunger controlling said second supply conduit means and said discharge conduit means, said valve plunger being adapted to assume a first switching position for admitting pressurized fuel from said pressure source to said servo pressure chamber and a second switching position for establishing communication between said servo pressure chamber and said discharge conduit means, (j) electromagnetic means for causing said valve plunger to move from one of its switching positions to the other, and (k) means for varying the angular position of said pump piston for altering the quantities of fuel injected by said assembly into said engine during the delivery strokes of said pump piston, the improvement comprising; A. a third supply conduit means extending from said pressure source to said valve plunger through which pressurized fuel is delivered by said pressure source for causing displacement of said valve plunger, B a solenoid valve in said third supply conduit means for controlling the admission of pressurized fuel to said valve plunger, said solenoid valve constituting said electromagnetic means, C means for intermittently energizing said solenoid valve, and D means to establish communication through a narrow throttle gap between said pump work chamber and said pressure source in the position assumed by said pump piston upon termination of its return stroke. 